Seismic cables and a method for manufacturing such

ABSTRACT

A seismic cable ( 1 ) and a method of manufacturing such a cable. The cable includes a plurality of elongated electrical/optical elements which are arranged to be interconnected with a number of seismic sensor devices arranged at intervals along the cable. A polymeric sheath and a protective outer armoring surround the elements to provide protection against radial stress of said cable. The sensor devices are installed outside of the elements and the armoring.

BACKGROUND OF THE INVENTION

The present invention relates to seismic cables in general and in particular to seabed laid seismic cables. Such cables are arranged to be installed in arrays to cover a certain area on the seabed. The seismic cables are designed to detect sound wave signals reflected from subsea oil and gas reservoirs when air guns are detonated in the sea.

The seismic cables include a number of sensor devices which are powered from a surface vessel. The array of seabed seismic cables may also include electronic units for signal processing. The cables therefore also include power conductors for the electronic units and for the sensors, as well as signal conductors for interconnections and transmitting processed signals detected by the sensors to the vessel.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved seabed laid seismic cable which can be manufactured in long lengths. The main features of the invention are defined in the accompanying claims. With this invention a type of seismic cable has been obtained, which is suitable for installation on the seabed and which can be connected in arrays.

BRIEF DESCRIPTION OF THE DRAWINGS

Above mentioned and other features and objects of the present invention will clearly appear from the following detailed description of embodiments of the invention taken in conjunction with the drawings where

FIG. 1 schematically illustrates a cross section of a cable,

FIG. 2 illustrates a cross section of the same cable where a sleeve surrounds the cable core,

FIG. 3 illustrates a side view of the said sleeve integrated in the cable corresponding to FIG. 2,

FIG. 4 illustrates a side view of the sleeve arranged on the seismic cable, —partially in section, and

FIGS. 5 and 6 illustrate the seismic cable with a housing for the sensor elements outside the cable armouring.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1—which is not drawn to scale—the sensor cable 1 corresponding to the invention includes power and signal conductors 5 (electrical and/or optical). These conductors 5 which may include pairs 6, quads 7 or other conductor elements 8 and 9 may be stranded helically or SZ-wise, but they may also be arranged axially.

All the conductors will be wrapped by a tape 10 made of a polymeric material and a protective inner sheath 11 made e.g. of thermoplastic polyester, which will be surrounded by an armouring 12, e.g. made of stranded steel wires. The interstices 13 in the cable core may be filled with a water blocking compound, such as petroleum jelly, the interstices 14 in the armouring are filled with a bitumen compound.

A seismic cable corresponding to the invention includes a number of electrical/optical elements 7, 8, 9 which are arranged to be interconnected with a number of seismic sensor devices, e.g. geophones and hydrophones, amplifiers etc., arranged at intervals along the cable. As corresponding to the invention these sensor devices are installed outside of the elements 5 and the armouring 12 at intervals along the cable there are arranged sleeves 15 (FIG. 2) surrounding the elements 5. These sleeves 15 consist of two interlockable halves 16 and 17 having at least one outlet 18 for electrical/optical elements 19 (FIG. 3) of the elements 5 in the cable core. To adjust the outer configuration of the sleeves 15 to the cable core covered by the sleeves at intervals these sleeves 15 have conical end portions 26, as shown in FIG. 3.

FIG. 4 illustrates the interlockable status of the two halves 16 and 17 having grooves 20 and tongues 21 to ensure a water tight connection when pressed together. Guiding means or studs 22 on the outer surface of the sleeve distribute the wires of the armouring wires 12 surrounding the cable (FIG. 1) as well as the sleeve (FIG. 2).

In accordance with the invention the sensor elements are to be installed outside of the armouring 12. Therefore, this armouring—at the location of the sleeve 15—is covered by a housing 23 (FIGS. 5, 6) within which the sensor devices 24 are integrated. The electrical/optical elements 19 inside the cable core and being guided through the outlet 18 of the sleeve 15 are to be interconnected with the sensor elements 24 inside the housing 23. The housing 23 and the sleeve 15 are e.g. interlockable by screws means 25 and known sealing means 27 (FIG. 3) between the individual parts to be connected will avoid any water penetration.

The above detailed description of embodiments of this invention must be taken as examples only and should not be considered as limitations on the scope of protection. The principles of the invention which have been described in connection with marine seabed laid seismic cables, can also be used in connection with towed seismic cables and on shore seismic cables. 

What is claimed is:
 1. A seismic cable (1) including a plurality of elongated electrical/optical elements which are arranged to be interconnected with a number of seismic sensor devices arranged at intervals along the cable, and with a polymeric sheath surrounding the elements and a protecting outer armouring surrounding said elements and providing protection against radial stress of said cable, characterized in that the sensor devices are installed outside of the elements and the armouring.
 2. A cable according to claim 1, characterized in that the sensor devices are installed in a housing arranged at intervals along the cable outside the armouring.
 3. A cable according to claim 1, characterized in that the polymeric sheath is replaced at intervals along the cable by sleeves surrounding the elements and having outlets for those elements to be interconnected with the sensor devices installed outside the armouring.
 4. A cable according to claim 1, characterized in that each sleeve consist of two interlockable halves having conical end portions.
 5. A cable according to claim 3, characterized in that the sleeves arranged below the armouring are interconnectable with the corresponding housing arranged above the armouring.
 6. A cable according to claim 5, characterized in that both the sleeve and the corresponding housing are provided with interlockable through-holes for the elements to be interconnected with the corresponding sensor devices in the housing.
 7. A cable according to claim 3, characterized in that each sleeve is provided with external studs for distributing the armouring wires on its outer surface.
 8. A method for manufacturing a seismic cable according to claim 1, characterized in that, after bundling or stranding with one another the elements and surrounding them by a sheath, the method comprises removing said sheath along the cable at intervals propose* for the arrangement of the sensor devices and replacing the removed sheath by sleeves, bringing elements to be connected with the sensor devices out of the sleeves through holes in said sleeves before providing said armouring to said cable, wherein the providing of said armouring around said cable comprises the step of stranding the armouring elements around the polymeric sheath as well as around the sleeves replacing the sheath at intervals.
 9. A method according to claim 8, characterized in that an excess of the elements in the area of the sleeves will be achieved by loops of the bundled elements and/or the lay length of the elements stranded with another.
 10. A method according to claim 9, characterized in that the elements are SZ-stranded with another. 